PROMERYCOCHCERUS 123 



build, although not as much so as in P. vatitasselensis. The more important differences in the front limb are: 

 the shorter humerus; the less pronounced olecranon process; the proximal lateral contact of the lunar with the 

 cuneiform; the lack of a firm contact between the lunar and metacarpal III, and the presence of a minute "facet" 

 on the trapezium. The hind limb is more elongated and is somewhat lighter in construction than that of P. carri- 

 keri. The tibia and the metatarsals, especially metatarsal V, are proportionately longer. The femur is more 

 elongated but is equally as robust. 



The whole skeleton has a proportionately short body and moderately long legs. 



Discussion: On the basis of the skeleton, the proportions of this species are exceedingly close to 

 those of P. gregoryi, and I should ally it with that form. The skull is nearly 100 mm. longer than 

 that of the type of the latter, which, if deducted from the total skeletal length of P. g. loomisi, gives 

 us a figure of 1380 mm. The total length of the skeleton of P. gregoryi is 1370 mm. 



There is a very interesting gradation of skeletal measurements from P. carrikeri to P. gregoryi 

 which is shown graphically in the following table: 



P. carrikeri 



Length of skull 316 



Length of skeleton 1720 



Height of skeleton 720 



Skeletal ratio \E^L 0.418 0.322 0.479 0.529 



Height 



Schlaikjer considers P. montanus grandis to be nearest to P. g. loomisi and states that it "forms 

 a splendid ancestral stage, structurally at least, for P. loomisi." Furthermore, he concludes: 



It represents an end member of a Promerycochoerus line which probably evolved from a large yet slender- 

 skulled Eporeodon species, such as E. montanus of the upper Oligocene, rather than from a more robust species 

 as E. occidentalis or the brachycephalic member E. trigotwcephalus, which exemplify a transmontane group that 

 inhabited the western coast of North America and which probably represent an ancestral stage in the Promery- 

 cochaerus superbus line. 



Promerycochcerus hesperus Stock 1930 

 Fig. 80 



Original Reference: Oreodonts from the Sespe deposits of South Mountain, Ventura County, Cali- 

 fornia. Carnegie Inst. Wash. Publ. No. 404, pp. 39-41, fig. 2 {Promerycochcerus ? hesperus). 



Type Locality: NE corner, SE }4> Sec. 13, T. 3 N., R. 21 W., San Bernardino Base line, in Morgan 

 Canyon, lower Santa Clara Valley, near Santa Paula, California. Univ. of Calif. Coll. Loc. No. A725. 



Geologic Horizon: Lower Miocene (upper Sespe). 



Type: Holotype, Cat. No. 27003 U.C.M., fragmentary right ramus. 



Specific Characters: This ramus belonged to a smaller animal than P. macrostegus or 

 P. superbus but about the size of P. hottandi hatcheri. The horizontal ramus is moderately deep, 

 and the inferior border slopes gradually downward and backward. The angle is prominent, the 

 narrow condyle is very slightly inset, the sigmoid notch is very shallow, and the coronoid process is 

 very short. 



Dentition: The metastylid of M a is medium in size. The molars lack any pronounced cingular 

 cusps between the hypoconids and protoconids. The premolars are crowded and are somewhat 

 overlapping. P 4 is typical of the genus, except that the normal small cusp-like enlargement on 

 the posterior crest is very small and appears more like a bifurcation than a cusp. P 3 is somewhat 



